This is a 371 of PCT/FR00/01835, filed Jun. 29, 2003.
The present invention relates to novel fluorinated benzodioxane imidazoline derivatives corresponding to formula 1. 
in which:
R represents a linear, branched or cyclized alkyl or alkenyl group containing 1 to 7 carbon atoms, or a benzyl group,
the fluorine atom on the homocycle can occupy position 5, 6, 7 or 8.
The invention relates to the racemic and enantiomerically pure forms, to the salified forms thereof and also to the process for preparing them.
The invention also relates to the use of these compositions as medicinal products, and also to the preparation of a medicinal product used as an xcex12-adrenergic receptor antagonist and intended in this respect to treat neurodegenerative diseases, and also their progression.
Advantageously, the radical R is a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an isobutyl group, a cyclopropylmethyl group, an allyl group or a benzyl group.
Preferably, the fluorine atom occupies position 5.
It has been shown (Mavridis, Neuroscience (1991), 41, 507) that the locus coeruleus plays a predominant role in the recovery of dopaminergic functions altered by administration of MPTP to monkeys. Its destruction brings about a reduction in recovery. Moreover, compounds with xcex12-antagonist action are shown as reducing Parkinson""s symptoms in monkeys (Colpaert, Brain Res. Bull., 26, 627, 1991) or in rats (Colpaert, Neuropharmacology, 26, 1431, 1987) by elevating the release of dopamine (Marien, M., Colpaert, F. Effect of (+)-efaroxan on mouse striatal dopamine metabolism in vivo. DOPAMINE 94-Satellite Meeting of the XIIth Int. Congr. Pharmacology, Quebec City, Canada, Jul. 20-24, 1994).
Furthermore, an xcex12-antagonist, idazoxan, is shown as having beneficial action on the deleterious effects of cerebral ischemia (Gustafson, Exp. Brain Res., 86, 555, 1991 et J. Cereb. Blood Flow Metab., 1990, 10, 885) and also in progressive supranuclear paralysis and neurodegenerative disease (Ghika, Neurology, 41, 986, 1991). It has also been shown that compounds with xcex12-antagonist activity induce an increase in the release of acetylcholine in the prefrontal cortex (Tellez, J.Neurochem. (1997), 68, 778).
Thus, a substance activating the noradrenergic system may have the property of opposing the progression of the degeneration of the involved neurons, by reactivating the various cerebral localization systems, whether they are dopaminergic or cholinergic, or whether this involves the release of growth factors (Fawcett et al. J. Neurosci. (1998), 18, 2808-2821). These compounds are thus useful in cases of neurodegenerative diseases of the type such as Parkinson""s disease or Alzheimer""s disease and their progression, Huntington""s chorea, amyotrophic lateral sclerosis, Creutzfeld-Jacob disease, progressive supranuclear paralysis, cognitive and memory disorders, attention deficit and vigilance deficit in the elderly, and also the progression or evolution of these diseases or disorders. Ischemic and post-ischemic cerebral disorders, cerebrovascular accidents and consequences thereof, depression, narcolepsy and male sexual dysfunctions are also concerned, as are disorders associated with acquired immunodeficiency syndrome.
It is known that benzodioxane derivatives such as idazoxan: 2-(1,4-benzodioxan-2-yl)-2-imidazoline, or alkoxy idazoxan: 2-(2-alkoxy-1,4-benzodioxan-2-yl)-2-imidazoline, have xcex12-antagonist properties (J. Med. Chem. (1983), 26, 823; J. Med. Chem. (1985), 28, 1054). These compounds have been patented in GB 2 068 376 for idazoxan and in EP 92328 for alkoxy-idazoxans.
It has been shown in these publications that a large number of idazoxan derivatives have been synthesized and tested for their agonist or antagonist action on the xcex11 or xcex12 receptors, inter alia, halogenated derivatives, substituted on the aromatic nucleus, have all been found to be less active than or inactive relative to their unsubstituted idazoxan analog (in particular the 6/7-fluoro, chloro or bromo derivative, 5,8-dichloro or 8-chloro derivative). Moreover, the 2-methoxy idazoxan derivative substituted in 6,7 with two methoxy groups showed only extremely marginal activity as an xcex12-presynaptic antagonist.
The compounds of the present invention differ from the known compounds in that they have a fluorine atom in position 5, 6, 7 or 8 of the aromatic nucleus. They have the property of being powerful xcex12-adrenergic receptor antagonists.
It has been found, remarkably, that the presence of this fluorine atom in these positions gives these molecules particularly advantageous properties when compared with their nonfluorinated analog.
The pharmacological properties of the products of the present invention have been studied, inter alia, in comparison with those of 2-methoxy idazoxan (RX 821002) and 2-ethoxy idazoxan (RX 811059), which are structurally related compounds that are derivatives not substituted on the aromatic nucleus.
Specifically, we show, in vivo, the superiority of the pharmacological properties of the products of the present invention in the test of memory deficit induced with scopolamine, of the antagonism of the hypothermia induced with guanabenz, an xcex12-agonist substance, and on the level, in the cortex, of normetanephrine, a metabolite and selective marker for the release of noradrenalin.
Test of the memory deficit induced with scopolamine:
In accordance with the cholinergic hypothesis of the phenomena of learning and memory, scopolamine has amnesiant properties in animals and man. Its administration to a healthy person induces certain amnesia symptoms similar to those observed in Alzheimer""s disease. It has been proposed that the scopolamine be used as an experimental pharmacological model of this pathology. The similarities between the memory deficits of Alzheimer""s disease and those induced with scopolamine in rats have been published (P. Chopin et M. Briley, The effects of raubasine and dihydroergocristine on an agerelated deficit in passive avoidance learning in rats, J.Pharm.Pharmacol. 42, 375-376, 1990). Scopolamine reduces the capacity for acquisition, memorization and recall in a test of passive avoidance in rats. This involves measuring the reticence, after learning, that the animal has in entering a dark compartment, where it receives a mild electric shock. The administration of scopolamine suppresses this reticence, and the test compounds oppose the effect of scopolamine.
The comparison of the products of the present invention is made with the known compound RX 821002, dextrorotatory enantiomer. The experimental protocol is that published by P. Chopin and M. Briley (Effects of four non-cholinergic cognitive enhancers in comparison with tacrine and galanthamine on scopolamine-induced amnesia in rats: Psychopharmacology, 106, 26-30, 1992).
The results are given in the following table:
The compounds of the present invention show appreciable activity over a wide range of doses, in contrast with (+) RX 821002, which is not significantly active. The amplitude of its effect is at least as large as that of tacrine, and more active than that of donepezil, reference compounds used therapeutically for Alzheimer""s disease.
The value and the appreciable difference of the products of the invention is thus shown.
Inhibition of the hypothermia induced with Guanabenz:
The assessment of the biological activity of the compounds of the invention is also carried out in vivo by studying the inhibition of the hypothermia induced with a central xcex12-agonist such as guanabenz according to the protocol of S. C. Dilsaver, Pharmacol. Biochem. Behav., 45, 247, 1993.
This test demonstrates the antagonist effect of the xcex12-adrenergic receptors, in vivo, of the compounds of the invention, and also their activity at the central level. The inhibitory capacities are expressed as the ED50 which represent the doses producing a significant inhibition of the hypothermia induced with guanabenz on the one hand, and a normalization, that is to say a return to the normal temperature for the animal, before injection of guanabenz on the other hand. These values are obtained using the method of J. T. Litchfield and F. Wilcoxon (J. Pharmacol. Exp. Ther., 96, 99, 1949). The comparison is made between the 2-methoxy compounds, fluorinated in position 5 (dextrorotatory compound of Example 1) and nonfluorinated: (+) RX 821002, and between the 2-ethoxy, fluorinated in position 5 (dextrorotatory compound of Example 2) and nonfluorinated: (+) RX 811059.
The greater power of action of the compounds of the invention compared with their analogs (+) RX 821002 and (+) RX 811059 is thus seen. The amplitude of the action is also demonstrated by the determination of the doses inducing the inhibition of hypothermia in 100% of the animals, on 6 doses (each dose separated by a factor of 4) for the dextrorotatory compound of Example 1 against 2 doses for (+) RX 821002. Similarly, the dextrorotatory compound of Example 1 normalizes the hypothermia in 100% of the animals on 3 doses, whereas (+) RX 821002 does not, it does so on only 80% of the animals and at only 2 doses.
It is thus seen that the products of the invention have a very broad range of active doses, and are thus better xcex12-adrenergic antagonists.
Release of noradrenalin:
The level of normetanephrine, a noradrenalin metabolite, in the cerebral tissues is used as a measurement of the release of noradrenalin. Wood, P. L. and coll. Pharmacological Rev. 40, 163-187, (1988), and J. Neurochem. 48, 574-579, (1987)). The formation of normetanephrine, by the action of catechol O-methyltransferase takes place on the outside of the noradrenergic neurones and its measurement takes account of variations in the release of noradrenalin. This measurement is performed in the frontal cortex, a region innervated mainly by the locus coeruleus.
The test compound is administered intraperitoneally to the mice, which are sacrificed after 60 minutes by irradiation with microwaves (to avoid any artefactual changes in the metabolite levels). After dissection, normetanephrine is assayed by HPLC on the cortical tissue extracts. At doses of 0.01 to 2.5 mg/kg, the assayed normetanephrine represents a level from 125 to 150% higher with the compound of Example 1, relative to (+) RX 821002, under the same conditions. This shows the greater efficacy of this compound compared with (+) RX 821002 for the release of noradrenalin.
Binding to the xcex12-adrenergic receptors in vitro:
It was also confirmed that the compounds of the invention have affinity for the human xcex12-adrenergic receptors, at the nanomolar level on the basis of tests of binding to the subtypes of these receptors, using tritiated 2-methoxy-idazoxan, [3H] RX821002, as radioactive ligand (J. C. Devedjian and coll. Eur.J.Pharmacol. (1994), 252, 43-49).
The in vivo tests show the advantage which may be afforded by substitution with a fluorine atom on the aromatic nucleus relative to the compound devoid of this substitution.
Since the compounds of the present invention contain an asymmetric carbon, they are in a dextrorotatory form and a levorotatory form. The present invention thus relates also to the enantiomerically pure compounds, to the addition salts thereof and also to pharmaceutical compositions comprising at least one compound of formula 1 and a suitable excipient. The pharmaceutical compositions may be presented in a suitable manner, for oral, injectable or parenteral administration, in the form of wafer capsules, gel capsules, tablets or injectable preparations, at a daily dose of from 0,1 to 200 mg.
The compounds of the present invention may be prepared from 3-fluorocatechol, (described in J.Amer.Chem.Soc. 77, 5314-5317, 1955) by coupling with 2,3-dibromopropionamide in acetonitrile in the presence of K2CO3 to give the 2 regioisomers 5- and 8-fluoro-1,4-benzodioxane-2-carboxamide. Several recrystallizations make it possible to isolate the 5-fluoro derivative in pure form, at the expense of the 8-fluoro derivative which is more soluble under these conditions. The amide function in position 2 of the benzodioxane is dehydrated into nitrile. This nitrile is then brominated by the action of NBS to give the bromonitrile, which is subjected to the action of a sodium alkoxide such as sodium methoxide in methanol, to form the intermediate imidate which reacts in situ with ethylenediamine to form the desired xcex1-methoxyimidazoline derivative. In a similar manner, the various alkoxy derivatives in position 2 are obtained by treating the preceding bromonitrile derivative by treatment with a corresponding alkali metal alkoxide.
The 2 enantiomers may be separated in several ways: either by diastereoselective crystallization with a chiral acid which may be tartaric acid or derivatives thereof such as dibenzoyltartaric acid, or by chromatographic separation, preparative HPLC, on a chiral phase, giving the dextrorotatory isomer and the levorotatory isomer, the hydrochloride of which may be obtained in crystalline form by the usual methods.
The 6- and 7-fluoro derivatives on the aromatic ring are obtained from (6- or 7-fluoro-2,3-dihydro-benzo[1,4]dioxin-2-yl)methanol, described in J. Med. Chem. (1987), 30, 814. These methanol derivatives are oxidized to acid and then amidated and dehydrated to nitrile according to the processes described in J. Med. Chem. (1983), 26, 823, or J. Med. Chem. (1985), 28, 1054, and then treated as indicated above.
The procedures for the various stages of the synthesis illustrate the invention: